Cyclodehydration of 2-mercaptoalkanols as a route to episulphides

Abstract

Intramolecular cyclodehydration of 2-mercaptoalkanols was previously known only in the case of 2,3-dimercaptopropanol. This reaction is shown to be undependable under the prescribed conditions, but to give good yields of 3-mercaptopropylene sulphide in the presence of an acidic catalyst. The acid-catalysed dehydration of simpler 2-mercaptoalkanols is shown to give 1,2-episulphides also, in yields which are in the reverse order of susceptibility of the products to acid-catalysed polymerization, but which even in the most difficult case studied may be raised to over 40% by a suitable choice of conditions. Potassium hydrogen sulphate was the preferred catalyst, because it caused less polymerization of the products than the other acids tried.